Shared-workspace groupware has not become common in the workplace, despite many positive results from the research lab. In this talk I will look at one reason for this lack of success: that most shared workspace systems are designed around the idea of planned, formal collaboration sessions, when much of the collaboration that occurs in a co-located work group is informal and opportunistic. To support informal collaboration, groupware must be designed and built differently. I will introduce the idea of community-based groupware (or Communityware), in which groupware is organized around groups of people working independently, rather than shared applications or shared documents. Communityware provides support for three things that are fundamental to informal collaboration: awareness of others and their individual work, lightweight means for initiating interactions, and the ability to move into closely-coupled collaboration when necessary.